25 Apr Purple Mozambique Garnet

Figure 1: Three purple rhodolite garnets tested by SSEF at the beginning of 2016, ranging in weight from 7 to 13 carats. Photo: SSEF

by Dr. W. Zhou, first published in Facette 23 (February 2017)

In early 2016, attractive bright purple garnets arrived at SSEF (Figure 1) in Bangkok, Basel and Hong Kong. Based on client information, they are from a new mine, Padagaga in the Chimoio area in Mozambique, which was discovered recently (Schwarz, 2016).

After routine gemmological testing, the chemistry of these garnets fits with rhodolite, within the solid solution series pyrope (Mg3Al2Si3O12) – almandine (Fe3Al2Si3O12). EDXRF analysis shows main chemical composition is around: Fe2O3 27%, MgO 17%, Al2O3 19% and SiO2 36% with minor amounts of CaO and MnO. Comparing this to published data (Lind, 2015, Schwarz, 2016 and Sangsawong 2016), the UV-Vis spectra (Figure 2) shows Fe2+ absorptions that dominate (around 500-700 nm, especially the ones from 500-600 nm) together with a mixture of Mn2+ (ca. 410 nm), while the contribution of V3+ + Cr3+ (420 to 430 nm and 515-530 nm) is relatively low.

Since this new material only recently appeared on the market, further studies are required to entirely understand the gemmological differences between this and stones from traditional localities like Tanzania and Malawi. We look forward to seeing many more such charming purple rhodolite garnets in the SSEF.